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Study of the gradation characteristics of backfill materials in underground mines along with evaluating the gradation of construction and demolition waste aggregate
Khandani, Atapour, Yousefi Rad, Khosh,
Volume 17, Issue 3 (12-2023)
Abstract
Backfill materials used to fill underground mines are a type of engineered material whose particle size distribution (PSD) directly affects their mechanical and physical properties. According to the authors' review, there is no comprehensive standard for the properties of aggregates used in underground mine backfill materials. In this paper, the particle size ranges and particle size distribution curves of various mine backfill materials, including hydraulic backfill, paste backfill and rock backfill, have been reviewed. The available data on different types of backfill materials were collected. Based on the collected data, the smallest particle size, the largest particle size and the PSD curve ranges for each type of backfill material were determined. Then the characteristics of the particle size distribution curve of each backfill material, including the mean particle diameter (D50), the uniformity coefficient (Cu) and the curvature coefficient (Cc), were calculated.  The results of the analysis of the PSD curves for paste backfill, hydraulic backfill and rock backfill materials showed that the particles in rock backfill and paste backfill had the largest and smallest sizes, respectively. Finally, the particle size distribution characteristics of a new backfill material prepared from construction and demolition waste (CDW backfill) are presented and compared with the particle size distribution of each of the conventional backfill materials. The results indicate that the PSD curve of the CDW backfill lies at the upper limit of the range of the particle size distribution curve of hydraulic backfill and at the lower limit of the range of the particle size distribution curve of rock backfill.
 

A comprehensive study on the effects of geometric and geomechanical parameters on crown pillar behavior during the transition from open-pit to underground mining
Salman Shamsoddini Motlagh, Saeed Mahdavi,
Volume 20, Issue 1 (6-2026)
Abstract
Due to the deepening of open-pit mines and associated environmental concerns, the current period has been termed the 'return to underground mining era'. One of the key factors in transitioning from open-pit to underground mining is designing crown pillars based on economic and technical considerations. Due to the uncertainties surrounding this research topic, the present study uses three-dimensional numerical simulations to investigate the interactive effects of geometric and geomechanical parameters on the behaviour of crown pillars during the transition to underground mining. Pillar behaviour was evaluated based on displacement magnitude and the volume of the plastic zone of the pillar. The results of the numerical simulation showed that geometric parameters play a much more significant role than rock mechanical properties. Of the geometric parameters, the pillar dimension index (the product of the pillar's thickness and span) and the crown pillar's span play a decisive role in controlling pillar behaviour. From a geomechanical perspective, within the range of variations considered in this research, the rock elastic modulus was identified as the parameter most influential on crown pillar behaviour. This parameter controls crown pillar behaviour at a critical value of 7 GPa. Crown pillar span was identified as the second most influential parameter and can predict crown pillar displacement with a correlation coefficient of 0.83. The pillar dimension index can estimate the plastic zone volume in the pillar with 20% accuracy.

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